BIO151 UNIT 4 CH. 53 POPULATION ECOLOGY

density

number of individuals per unit area or volume

dispersion

pattern of spacing among individuals within the boundaries of the population

immigration

the influx of new individuals from other areas

emigration

the movement of individuals out of a population & into other locations

territoriality

the defense of a bounded physical space against encroachment by other individuals

patterns of dispersion

clumped

uniform

random

clumped dispersion

the most common pattern of dispersion in which individuals are aggregated into patches

plants & fungi are often clumped where soil conditions & other factors favor germination & growth

it can also increase the effectiveness of predation or defense

uniform dispersion

an evenly spaced pattern of dispersion which can result from direct interactions between individuals in the population

ex: plants secreting chemicals that inhibit the germination & growth of nearby competing individuals

animals exhibit this through territoriality

random dispersion

an unpredictable spacing pattern of dispersion in which the position of each individual in a population is independent of other individuals

occurs in the absence of strong attractions or repulsions

ex: dandelions randomly distributing windblown seeds in a habitat that’s uniform

demography

the study of key characteristics of populations & how they change over time

life table

summarizes the survival & reproductive rates of individuals in specific age-groups within a population

cohort

used to construct a life table

a group of individuals of the same age that are tracked from birth until death

if the species is sexually reproducing, usually the males are ignores and the females are recorded due to only them producing offspring

survivorship curve

a plot of the proportion or numbers in a cohort still alive at each age

how are reproductive rates recorded?

direct counts & the mark-recapture method, more recently molecular tools

the output is measured as the average number of female offspring produced by a given age-group of females

exponential population

when a population experiences such an ideal condition, it increases in size by a constant proportion at each instant in time

intrinsic rate of increase

the per capita rate at which an exponentially growing population increases in size at each instant in time

carrying capacity

symbolized by K

the maximum population size that an environment can sustain

limiting resources can include energy, shelter, water, refuge from predators, and pathogens

life history

the traits that affect an organism’s schedule of reproduction & survival

evolutionary outcomes reflected in its development, physiology, & behavior

semelparity

a “one-shot” pattern of big-bang reproduction

ex: coho salmon hatches in freshwater streams, heads to the Pacific Ocean to mature for a few years, heads back to the same stream to produce thousands of eggs then dies

this can be an adaptation to harsh environments, as the species uses all of its resources to reproduce as much as possible before death in one single “spurt”

iteroparity

repeated reproduction

ex: a female loggerhead turtle produced 4 clutches, roughly 300 eggs/year, then it waits 2-3 years before laying more eggs

the theory goes that the turtle doesn’t have sufficient resources to produce that many eggs per year

K-selection

selection for traits that are advantageous at high densities

r-selection

selection for traits that maximize reproductive success in uncrowded environments

density independent

birth or death rate that doesn’t change with population density

density dependent

death rate that increases with population density or a birth rate that decreases with rising density

mechanisms of density-dependent regulation

competition for resources

disease

intrinsic factors

territoriality

toxic wastes